1 rotor = half the gas consumption of two ?
 

I was wondering why they haven't considered using the rotary in a more economical and cheaper car, ...I'm by now means an engineer, but was wondering if a 1 rotor rotary would suffice for this ?

120hp and around 30mpg ? This would definitely do for most cars, ...and...maybe cheaper to produce?

Jarred...you got me!! Maybe if it was a 10 rotor we would have 2380 HP? Seriously, I think your though process is a little off.

- Irish

I know it's off, it has to be, :) I was jsut wondering if a one rotor was possible, and if maybe it would be better on the gas, and or cheaper to produce ?

In the sense that anything is possible, it's possible. As I recall, the Mazda rotary prototype was a single rotor.

Since Mazda is the only auto manufacturer building rotaries it is totally up to them whether another, smaller version ever gets built and sold.

IMHO, it isn't going to happen. Alternative (and yes sometimes quirky) powerplants are going to be very hard to market to the low end of the market. People who buying at the low end want cheap to buy, cheap to maintain, reliable transportation. they don't really care what's under the hood. The rotary is a selling feature in a high-end sports car. In an economy car it would be "so what".

I'll take out a rotor from my 8 tomorrow and report my gas mileage back to you. ;)

using your equation, would you want a 119hp, 78ft/lb single rotor coupe while a similarly priced (i'd guess) 2+2 entry coupe would feature a large displacement 4 cylinder engine making anywhere from 130-160hp, AND 120+ft/lb of torque??

the 2 rotor is already barely 'practical', would anyone looking in the 'value' class of cars even consider it??

you're barking up the wrong tree if you want economy with a rotary. It wouldn't make sense to do the R&D for it when a 4 cyc car would beat it hands down.

My understanding is that the dual rotor is far superior to the single in ways other than it uses double the gas. First, I believe the single rotor motors are not balanced like the doubles, and thus would need some sort of a harmonic balancer. Not to mention it wouldn't be nearly as smooth since it'd be firing half as often.

Ahh, a dreamer like me...LOL

A rotary weighs more than a I-4 yet less than some V-6 & probably all V-8's. So, for a small car it would probably not be a good choice. Also, as others have said, considering that the rotary is still not as efficient with fuel as I-4's, most V-6, and heck even a few V-8's why put it into another car other than a sports car?

The weight savings, layout, and HP per size is a good thing while us rotary owners can close our eyes to the fuel ecnomy because well...it's expected. I don't think I would build rotaries if I owned a car company (just not worth the money and effort needed) and that is why Mazda is alone in the rotary department.

Honestly, I wish more companies got involved so there could be a chance for a breakthrough with the old rotary...and I still hope and dream about it, but it seems it might always be just a special motor but not a common or efficient one.

One bright side, they (Mazda and some others) say Hydro fuel really works well with the rotary engine so maybe it's the "OLD" engine design of the future...LOL, maybe the rotary was just created before it's time...in cars that is.

btw, there were threads a few months back about getting the rx8 to turn off half of the engine for better fuel economy at crusing speeds. You'd have to do a search to find it.

4 cyl half the gas of V8? V8 2x HP than 4? Not quite.

Honestly, I believe if Mazda stays on it and gets more support on it, the rotary could very easily become a good choice for a motor. Sure it doesn't get good gas mileage, but that could easily be improved with some studies. I would take this motor and have some serious experiments done with it. I think it could be a great motor for all cars... maybe not trucks or SUVs due to the lack of low end, but definitely cars.

Ok, just realized I was a little off subject so just ignore this post. :D

Last summer I rigged my RX-7 up to run on 1 rotor at the flick of a switch because I had the same question. What I found was that it had far less than half the power of 2 rotor mode and it vibrated like crazy. Max speed floored was about 50 mph. My engine is ported too. If you tried to accelerate in 1 rotor mode, you'd lose a race to a Geo Metro who started out in 5th gear. It is that bad. I had postulated that even if a slightly rich a/f ratio was needed in 1 rotor mode to keep it running, that it would still be less fuel than for 2 rotors. I'm not sure how that worked out though since the car wasn't fast enough for freeway use and to shut a rotor off on any other form of road was for such a short time that it didn't do anything useful. The project was abandoned.

hmmm....thats interesting, ..you think if they designed the engine for one rotor from the ground up they could get different results ? my only reasoning is, ...that engine was designed for 2 rotors, ...maybe something could be different. ...

awsome test though...

What needs to be done is a comparision between the Mazda rotary and 4, 6, and 8 cylinder engines with similar horsepower and vehicle weights. I'm pretty sure you won't see a huge difference in fuel consumption. I've heard lots and lots of horror stories on here about the gas milage of the RX-8, but so far mine does between 19-23 in mixed driving.

When you say that you rigged it by the flip of a switch, what exactly did you do? Shut down the fuel injectors or shut down the ignition or both?

Remember, all the piston engines with variable displacement kill the compression in the dead cylinders by leaving the exhaust valves open so there is no compression (in addition to killing the fuel injection and ignition).

In a rotary (standard anyway) there's no way to kill the compression in the unused rotor so you are using half the power just to overcome the compression of the dead rotor.

Actually in the variable piston engines, they leave all the valves closed, not open so in essence it is like a spring. Unfortunately I can't simulate that. I just shut off fuel to that rotor. Ignition was pointless so no need to kill it.

Yea, but you're still swinging around all the extra weight while not producing any power doing so.. in a single rotor engine (designed to be 1 rotor), you could possibly use less gas and get 1/2 the power as you dont have that extra weight to sling around, but you also dont have the power 180 degrees apart from the second rotor.

I dont know if that lack of power 180 degrees out of phase would be overcome by the lack of rotating mass..

RG? that make sense?

In a variable displacement piston engine, the others still have to move the nonworking ones as well.

I do feel that a dedicated 1 rotor engine would work better than the way I tried it. I just don't feel it is feasible to shut down a rotor for economy reasons as with some piston engines. For economy, maybe a turbo 1 rotor??? You could still get over 200 hp out of it.

interesting point, but they also shut down pistons in pairs in the V engines so that they're never off balance like you would be in a 2 rotor engine.. They're still moving the dead weight around but they're also still producing 2/3 of the power and only slinging an extra 1/3 of the weight whereas we'd be producing 1/2 the power and slinging an extra 1/2 the weight..

In a 2 rotor, each rotor is 180 degrees out from the other. How is shutting one down throwing it off? This would be a problem in a 3 rotor.

50% of the power comes from that 1 rotor though and it's 50% additionaly weight to carry around.. It's still rotating mass no matter where it is in phase, right? so it still counts as extra work that one rotor has to do, plus the e-shaft was balanced to have 2 working rotors, wasnt it?

I think a 3 rotor would actually work better. You drop the center rortor, lose 1/3 the power, 1/3 the extra mass the other 2 would have to carry.. so they're still producing 66% of the power they would normally and saving maybe 25-30% of the fuel.

the rotors in a 3 rotor are 120 out of phase, right? so if you kill the middle, the 2 ends are like 240 out of phase.. that could be bad too, lol.

Nope - doesn't work that way.

Your car requires a certain amount of energy to move and maintain speed. That requirement doesn't change just because you have a smaller or bigger powerplant. I went into details in this thread (third last post, dated 01-04-2005), talking about the energy requirements.

Basically, you can run a more efficient engine to produce the required power, but you're only talking a few percent difference in efficiency, not 50% less. Further, acceleration requires different operating constraints, and history has shown that often the more powerful optional engine in a car gets better fuel efficiency than the less-powerful base engine because it spends less time at full throttle, so more time operating in a more efficient range.

Regards,
Gordon

You just need 2 throttle bodies and you're all set, otherwise you're running a giant air compressor for nothing.

It's not the extra weight that is a problem, it's the extra friction. (Slinging around weight doesn't require energy as long as it's kept at a constant speed.)

One rotor at high throttle setting requires less fuel than 2 rotors at low throttle setting, assuming both produce the same amount of power.
Also when you accelerate at full throttle in a high gear you need less fuel than when you accelerate at partial throttle in a low gear (same power).

However you still have to deal with that extra vibration. Another reason for the flywheel generator/motor that could reduce that vibration (that's what Honda is using it for too).